= Heat generation rate
{title2=$\dot Q$}
A <heat generation rate> specifies the <power> deposited into microscopic thermal degrees of freedom, usually through conversion of electrical, chemical or mechanical <energy>. Its unit is the <watt>. The term is used as a source in a thermal <energy> balance; it does not imply creation of total <energy>.
A resistor supplied with current $I$ has electrical <power> $I^2R$ converted by <Joule heating>. If that <power> is deposited approximately uniformly in a body of <volume> $V$, the <volumetric heat generation rate> is $q'''=I^2R/V$. A steady body can export the same total <power> through <heat transfer> and retain constant <temperature>. If it is approximately isolated for a short interval, the deposited <energy> instead raises its <internal energy>, giving $C\dot T=P$ when its <heat capacity> is approximately constant.
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